Method and arrangement for improving the angular resolution of a monopulse radar

ABSTRACT

The invention relates to a method for improving the angular resolution of a monopulse radar. 
     Starting from the sum signal S, a direction signal θ b , and a signal representing the quadrature angle-error measurement |ε q  ε, the method consists of calculating in a first device 201 a signal Δθ representing the wingspan of the target, then of calculating in a second device 202 two measuring signals θ A  and θ B  representing respectively the direction of the external limits of the target, as well as a signal Q representing the quality of these measurements and finally of carrying out an adaptive filtering operation on the measurements in a third device 203, in order to obtain filtered estimates for Δθ, θ A  and θ B .

BACKGROUND OF THE INVENTION

The present invention relates to a method which permits the resolutionof a monopulse radar to be improved by processing the various signalswhich are obtained, in the conventional manner, in a radar of this type.The invention likewise relates to an arrangement which can be assignedto a monopulse radar in order to implement this method.

It is known that, with the aid of two receivers which are arranged in amanner such that their axes of reception are slightly out of alignmentwith the axis of transmission, a monopulse radar is capable of providingtwo separate signals, one of which corresponds to the sum of the signalsreceived by the two receivers and gives the same indications as aconventional radar, while the other signal corresponds to the differenceof these two signals and gives a difference-signal which enables theerror-angle between the direction of the detected target and the antennaaxis to be measured.

When the detected target is complex and is composed of severalreflecting zones, known as bright points, either because of its shape orbecause of the fact that it is composed of several separate objects, thesignals delivered by the monopulse radar are observed to be subject tosignificant fluctuations. These fluctuations, known as glint, are due tointerference effects between the waves, which are reflected by thevarious bright points, and are capable of giving rise to incorrectindications or even grossly misleading indications.

Two distinct types of arrangement have been used in order to avoid thisphenomenon.

The first type of arrangement, corresponding for example to FrenchPatent 2,396,311, in the name of the Applicant Company, is known as anantiglint device. It utilizes the strong correlations between the sumchannel, a conventional angle-error channel and an additionalangle-error channel, which is called quadrature angle-error channel andcorresponds to the imaginary part of the complex difference-signal, thereal part of the latter corresponding to the conventional angle-errorchannel.

These correlations enables an effective adaptive-filtering procedure tobe set up, which enables a direction to be determined, corresponding infact to the center of mass of the bright points of the target.

When this target is on its own, this center of mass is, as a rule,situated inside the target, this fact justifying the interest inantiglint devices of this nature, of which numerous embodiments areknown.

However, no further information are available regarding the dimensionsof the detected target, which would be particularly important if thetarget is composed of several separate objects, such as aircrafts makingup a squadron. The ultimate objective is to open fire at theseaircrafts; but in this case there is every chance of firing at emptyspace: For example a missile which is guided by a device of this typewill pass between two aircrafts, which are detected simultaneously,without touching either of them.

The second type of arrangement utilizes the fact that the bright pointsof a target approach or move off with a velocity relative to the radarantenna, corresponding to a Doppler effect which is particular to eachbright point. The velocity of each bright point is associated with itsposition in the target, and the analysis of the Doppler spectrum fromthe whole of the target may therefore make it possible, at least intheory, to measure the velocity of each of the bright points and thus toreconstitute the overall dimensions of the target.

In order to obtain this result, it is nevertheless necessary to carryout a highly discriminatory spectral resolution procedure on the Dopplerspectrum of the received signal, this procedure on the one hand beingvery difficult and on the other hand necessitating a very large numberof calculations which have to be performed very rapidly: This secondmethod has not given rise to satisfactory embodiments.

the invention proposes to process the fluctuations in the angle-errorsignals in order to extract from then the information corresponding tothe external dimensions of the target, without seeking solely to reducethese fluctuations, as in the case of the conventional antiglintdevices. For that purpose, a model of the target is produced, byreducing it to the two principal bright points at the greatest distancesfrom its center of mass. By then processing simultaneously the sumchannel, the conventional angle-error channel and the quadratureangle-error channel between two consecutive extreme values of the sumchannel, a measurement of the wingspan of the target is obtainedtogether with a measurement of the directions of the two bright pointsrepresenting the target.

SUMMARY OF THE INVENTION

In the method according to the invention, starting from sum signal S,direction signal θ_(b) and quadrature angle-error signal εq, thefollowing operations are carried out in order to obtain a signal Δθwhich is a measurement of the wingspan of the target:

detection of two successive extreme values of S: S max and S min;

measurement of the time interval ΔT separating S max from S min;

integration of |εq| over the time interval ΔT;

division by ΔT of the result of this integration, in order to obtain themean value of |εq|, namely |εq|, over the time interval ΔT;

calculating of a coefficient ##EQU1## multiplication of k₁ by |εq|,which operation yields the value of Δθ.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will clearly appear fromthe following description presented by way of a non-limiting example andwritten by reference to the figures which are attached and in which:

FIG. 1 represents the block diagram of a known monopulse radar, thisdiagram enabling the quantities and the signals utilized in theinvention to be defined;

FIG. 2 represents the block diagram of an arrangement according to theinvention;

FIGS. 3a, 3b and 3c represent respectively the block diagram of thecircuit 201 shown in FIG. 2 and two curves which represent the inputsignals of this circuit;

FIGS. 4a, 4b and 4c represent respectively the block diagram of thecircuit 202 shown in FIG. 2, and two curves which represent inputsignals of this circuit;

FIG. 5 represents the block diagram of the circuit 203 shown in FIG. 2;

FIG. 6 represents a detailed embodiment of the circuits 301, 303, 304,305 and 401 shown in FIGS. 3 and 4;

FIG. 7 shows a curve representing the signal S over a time intervalsufficient for defining the signals used in the description of the modesof operation of the circuits shown in FIG. 6;

FIG. 8 shows curves representing the experimental measurements of thesum and difference signals, and the estimation of the externalboundaries of the target.

DESCRIPTION OF PREFERRED EMBODIMENTS

In a monopulse radar--the diagram of which is reproduced in FIG. 1 inwhich definitions of the quantities to be measured have likewise beenrepresented--the measurements take place in two planes, as a rule inelevation and bearing, in order to locate the target in space. These twoplanes are treated in the same way and the remainder of this descriptionhas therefore been limited to only one of these planes, it beingunderstood that for the other plane the corresponding arrangement andtreatment are identical.

On the FIG. 1 an antenna 100 is defined by two perpendicular axesX_(ant) and Y_(ant) which are associated with it. It is mobile within aplane XOY defined by two fixed axes.

The orientation of the antenna is measured by an angle θ_(ant), betweenthe axes X and X_(ant), and the direction of two elementary targets orbright points A and B, which have been detected by the radar, ismeasured, relatively to the axis X, by the angles θ_(A) and θ_(B)respectively. The direction of the radioelectric center of mass of thetwo bright points A and B, corresponding to the direction measured by adevice of the antiglint type, is measured by the angle θ_(b), relativelyto the axis X. In the coordinates of the axes which are associated withthe antenna, this angle θ_(b) corresponds to the angle ε_(r).

The signals received by the antenna are processed in the receptioncircuits of the radar 101, which delivers signals representing a sumchannel S and a difference channel Δ (the arrow indicating that complexquantities are involved).

These two channels are processed in an angle-error signal receiver 102,which delivers on the one hand a sum signal S and on the other hand acomplex angle-error signal: ##EQU2##

in which formula the * sign in the exponent designates the conjugatevector.

This complex angle-error signal is processed in two circuits 103 and 104which are capable of delivering respectively the signals correspondingto the real and imaginary parts of the complex signal.

The real part ε_(r) is the conventional angle-error signal which isprovided by the known monopulse radars.

The imaginary part ε_(q) is a signal called quadrature angle-errorsignal.

It is known that the signal ε_(r) in fact is a measurement of theangular deviation of the target and more precisely of the radioelectriccenter of mass of the target relatively to the antenna axis. As thisdirection varies during the radar tracking process the value θ_(b) ofthe angle between the direction of the target and the fixed axis OX willbe used in the remainder of this text.

Relative to this axis, the direction of the antenna is given by angleθ_(ant). The direction signal θ_(b) is therefore obtained from therelationship:

    θ.sub.b =ε.sub.r +θ.sub.ant

A measuring signal θ_(ant) can be obtained starting from the antennaorientation servomechanism 105, for which the transfer function isobtained, by using the Laplace transform, by the formula ##EQU3## Thisservomechanism 105 operates from the input signal ε_(r) and delivers asignal which controls the antenna-orientation motors and whichrepresents a measurement of θ_(ant).

Under these conditions, θ_(b) will be obtained by means of the formula:##EQU4##

When the pattern of the target is formed by two bright points A and B,the directions of which are measured by the angles θ_(A) and θ_(B)relative to the axis OX, the complex sum and difference signalscorresponding to the radioelectric center of mass of these two brightpoints can be expressed as follows:

    S=m.sub.A +m.sub.B e.sup.jΔφ

    Δ=m.sub.A (θ.sub.A -θ.sub.ant)+m.sub.B (θ.sub.B -θ.sub.ant)e.sup.jΔφ

in which expressions m_(A) and m_(B) are the respective reflectioncoefficients at the bright points, and Δφ is the phase-differencebetween the waves reflected by these points.

θ_(b) is obtained by summing ε_(r) and θ_(ant) in the adder 106.

this enables the values of S, ε_(r), ε_(q) and θ_(b) to be calculated,which are given by the expressions: ##EQU5##

It is clear that these measurement fluctuate as a function of thevariations in Δφ, these variations precisely corresponding in fact tothe well-known phenomenon of glint.

Moreover, it is observed that the quadrature angle-error signal ε_(q) isproportional to the angular deviation Δθ=|θ_(A) -θ_(B) | separating thetwo bright points.

By processing the channel carrying the quadrature angle errormeasurement, the invention permits a measurement of Δφ to be obtained.Starting from this measurement the invention then permits, by utilizingthe sum channel and the angle-deviation θ_(b) the position of the pointsA and B to be completely reconstituted.

An arrangement which enables this processing to be carried out isrepresented in FIG. 2.

It includes a first circuit 201 which permits the wingspan of the targetto be measured, starting from the amplitude S of the sum signal and fromthe modulus of the quadrature angle-error measurement, obtained byrectifying of the signal ε_(q). This measurement of the wingspan isdelivered in the form of a signal Δθ.

A second circuit 202 makes it possible to measure the directions of thetwo bright points on the exterior of the target, which represent intheory its external boundaries. This measurement is carried out from thesignal Δθ supplied by the circuit 201, from the signal S and from thesignal θ_(b), which measures the direction of the target. Themeasurements of the directions of the two bright points are delivered bythe circuit 202, in the form of two signals θ_(A) and θ_(B). At the sametime, the circuit 202 supplies an estimation of the quality of these twosignals, in the form of a quality signal Q.

As the signals which are provided by the circuits 201 and 202 arethemselves affected by significant fluctuations, they are subjected in acircuit 203 to an adaptive-filtering procedure which is capable ofproviding a filtered estimation of these measurements, in the form ofthree signals Δθ, θ_(A) and θ_(B). The matching of this filter isadjusted by varying its gain, under the control of the quality signal Q.

Calculation shows that, between two successive extreme values of thesignal S, which are denoted S max and S min, the mean value of therectified quadrature angle-error signal ε_(q) is defined by theexpression: ##EQU6##

Δθ can therefore be expressed in terms of ε_(q), S_(max) and S_(min) bythe formula: ##EQU7## this formula explaining the processing which isperformed by the circuit 201 in FIG. 2.

An embodiment of this circuit 201 is represented in FIG. 3a withreference to the FIGS. 3b and 3c, which represent the variations of thesignals S and ε_(q) as a function of time, with the indication of thepoints between which the measurements are made.

The signal S is applied to a circuit 301 which enables the extremevalues of this signal to be detected, and which also contains twomemories, one of which is assigned to the value S max and the other tothe value S_(min).

Starting for example at an instant t (S max), at which S attains thevalue S max, the memory containing this values is set, while theinformation stored in the other memory is continuously updated bysuccessive values of the signal S, up to the instant t (S min) at whichthe circuit detects that S is passing through the value S min.

At this instant, the two values, S max and S min, which are thenavailable, are transmitted to a calculating circuit 302 which determinesa coefficient k₁, such that: ##EQU8## Such a calculation is extremelysimple and can be carried out for example by means of a suitablyprogrammed microprocessor of type 6800.

After this instant, the memory assigned to S min is set, while theinformation stored in the memory assigned to S max is updated by thesignal S, until the new signal S max is detected.

In the process of detecting the extreme values, the circuit 301determines on its own the instants t (S max) and t (S min). Theseinstants are transmitted to a circuit 303 which synthesizes controlsignals which permit the functioning of the whole of the arrangement tobe synchronized.

In order to obtain the mean value to the modulus of ε_(q) (required forthe calculation of Δθ), an integrator 304 is used which receives on theone hand the rectified signal ε_(q) and on the other hand the signalsfrom the control circuit 303 which indicate to it the instants betweenwhich the integration is to be performed.

An example of the signal ε_(q) is given in FIG. 3c, where it will benoticed that this signal comprises a negative portion delimiting an areaI₁ and a positive portion delimiting an area I₂. The integrationconsists of performing the calculation of these two areas and of addingthem in order to obtain the signal A=|I₁ |-I₂.

By comparing the signals t (Smax) and t (S min), the integrator likewiseprovides the duration ΔT between these two instants. This duration isavailable for the adaptive-filtering circuit 203, and enables the meanvalue of |ε_(q) | to be calculated in a divider 305, this value beingequal to ##EQU9##

Since therefore this mean value and the coefficient k₁ are thusavailable the wingspan Δθ of the target is obtained by forming in amultiplier 306 the product of the output signals of the computer 302 andof the divider 305.

The calculation shows that the directions of the bright points on theexterior of the target are associated with the values of the measureddirections θ_(b) of this target at the instants when the sum signalpasses through extreme values. The measurements θ_(A) and θ_(B) of thesedirections are then given by the formulae:

    θ.sub.A =θ.sub.b (S max) +k.sub.2° Δθ

    θ.sub.B =θ.sub.A -Δθ

Where the coefficient k₂ is given by: ##EQU10##

FIG. 4a represents an embodiment of the circuit 202 of FIG. 2, whichenables the angles θ_(A) and θ_(B) to be calculated. FIGS. 4b and 4c,represent respectively the variations of S and of θ_(b) as a function oftime, with the indications of the points between which the measurementsare made.

A first circuit 401, containing two memories, receives the signal θ_(b)and from the circuit 303 a control signal which indicates the instantsat which the signal S assumes the values S max and S min. This enablesthe storage of the values of θ_(b) at these instants, namely θ_(b)(Smax)and θ_(b)(Smin).

A comparator 402, compares these values and delivers a signal s whichhas the value +1, if θ_(b)(Smax) exceeds θ_(b)(Smin), and -1, if theopposite occurs.

This signal s, together with the signals S max and S min coming from thecircuit 301 shown in FIG. 2, are applied to a circuit 403 which enablesthe coefficient k₂, defined earlier in this test, to be calculated.

In order to effect this calculation, S min and S max are applied to adivider 413, which proceeds to calculated ##EQU11## and delivers asignal a which represents the result of this calculation. The signal sis multiplied by a signal which has a constant value of 0.5 in amultiplier 423 and the result of this operation is applied to amultiplier 433 which likewise receives the signal a. Finally asubtracter 443 receives at its positive input the signal which has aconstant value of 0.5 and which is also applied to an input of themultiplier 423, and at its negative input the output signal from themultiplier 433. The desired coefficient k₂ is therefore obtained at theoutput of this subtracter 443.

The signal θ_(b)(S max) delivered by the circuit 401 is likewise appliedto a circuit 404, which also receives the coefficient k₂ and the signalΔθ which is obtained at the output of the multiplier 306 shown in FIG.3.

In this circuit 404 the signal Δθ is multiplied by the coefficient k₂ ina multiplier 414. The result of this multiplication is added, in anadder 424, to the signal θ_(b)(S max) and this adder delivers the signalθ_(A), which measures the direction of the bright point A.

This signal θ_(A) which is available at an output of the circuit 404 islikewise applied in this circuit to the positive input of a subtracter434 which also receives the signal Δθ at its negative input. Thissubtracter delivers the signal θ_(B), which measures the direction ofthe bright point B.

As the signal a is available in the circuit 403 this circuit alsocalculates relatively to the measurements performed aquality-coefficient which is defined by the expression ##EQU12## Inorder to effect this calculation, the signal a is inverted, in aninverter 453, and is then applied to a multiplier 463 which alsoreceives the signal S max and delivers the signal Q.

The quality-coefficient Q is an effective indication of the quality ofthe measurements, as in fact it depends directly on the quality of theselection of the extreme values on the sum channel: the higher the ratioof a maximum value to a minimum value on this channel is the better theselection. Moreover, this quality is improved in proportion to thesignal/noise ratio and when the measurements therefore correspond for agiven ratio ##EQU13## to a maximum value of S max. Thus, by taking theproduct of the ratio ##EQU14## and of S max, the resulting valueeffectively maximizes the two criteria which have been defined in theabove manner.

The adaptive-filtering device 203, which is capable of delivering afiltered estimation of the values of Δθ, θ_(A) and θ_(B) can be realizedas shown by FIG. 5.

This device incorporates a first circuit 501 which, starting from thequality-coefficient Q, and from the time ΔT separating two successiveextreme values, enables the gain-value k₃ of the adaptive filters to becalculated: It allows the measurements to be estimated.

A second circuit 502 incorporates three identical adaptive filters 512,522 and 532, each of which permits the filtering of one of the threemeasurements respectively. These filters are of the type known as Kalmanfilters.

Describing for example the filter 512, the signal Δθ is received at aninput, and the signal Δθ is delivered at the output which represents afiltered estimated value of Δθ. In addition, this signal Δθ is applied,within the filter 512, to a variable-delay line 513, the delay producedby this delay line being controlled by the signal ΔT which representsthe time separating the two previous extreme values. This delay linetherefore delivers a signal Δθ (t-ΔT) which represents Δθ at the instantΔT earlier. The signal Δθ is applied to the positive input of asubtracter 514 which also receives, at its negative input, the outputsignal from the delay line 513. The subtracter 514 thus compares the newmeasurement of Δθ, at the instant t, with the value of the estimate ofΔθ at the instant t-ΔT. The output signal from this subtracter 514 isapplied to a multiplier 515, in which it is multiplied by thecoefficient k₃ obtained by means of the circuit 501. The output signalfrom this multiplier is added to the output signal from the delay line513, in an adder 516, which delivers the desired estimate value Δθ.

Under these conditions, the estimated value of Δθ is given by theequation:

    Δθ (t)=[Δθ(t)-Δθ(t-ΔT)]°k.sub.3 (t)+Δθ (t-ΔT)

The variable-delay line enables the effective value of the estimateobtained in respect of the preceding extreme value to be used in thecalculation and not an intermediate value, since the time ΔT betweenthese extreme values varies continuously.

This recurrence-equation can be written in the following form:

    Δθ(t)=Δθ(t) X k.sub.3 (t)-Δθ(t-ΔT)[1-k.sub.3 (t)]

which enables the effect of the coefficient k₃ to be taken into accountmore effectively.

When, at an instant T, the measurement is very good, that is to say whenQ(t) is very high, k₃ (t) should be such that the estimate is very closeto the measured value Δθ(t). This condition will be satisfied if k₃ isvery nearly equal to 1.

conversely, if the measurement is very bad, corresponding to a low valueof Q(t), it is necessary to minimize the weight of this measurement inthe new estimate, and to maximize the previous estimate. This conditionwill be satisfied if k₃ has a value which is nearly equal to 0.

In fact the quality of the measurements varies between these twoextremes and the coefficient k₃ is hence constrained to assume a valueranging between 0 and 1.

Since mereover the measured quantities change in the course of time, forexample in accordance with the presentation of the target with respectto the antenna axis, without these changes corresponding to statisticalfluctuations of the measurements, it is necessary, in the calculation ofthe coefficient k₃, to assign more importance to a recent measurement,even if of medium quality, than to an older measurement, even if thequality of the latter is very high.

In order to obtain that effect, the signal Q is applied, in the circuit501, to one input of an adder 503. The output from this adder is appliedt a delay line 504, the delay produced by this delay line being adjustedby the signal ΔT, which makes it possible to take into account themeasurement corresponding to the previous extreme value. The signalleaving this delay line is multiplied, by means of an amplifier 505, bya coefficient G which can vary between 0 and 1 and is then applied tothe second input of the adder 503. As a result, the signal Q_(r) leavingthe adder 503 is equal to the sum of the signal Q and of all thepreceding signals, each of which has been weighted by a coefficient,equal to G raised to a power corresponding to the previous rank of thesignal. As G varies between 0 and 1, the influence of the earlier valuesof the coefficient Q dies away rapidly.

In order to satisfy the condition according to which the magnitude ofthe coefficient k₃ should be between 0 and 1, a divider 506 is used,which enables Q to be divided by Q_(r) and which delivers the signal k₃.

From this description, it becomes clearly evident that the effectivefunctioning of the whole arrangement depends on the correct selection ofthe instants at which the sum channel passes through the maximum andminimum values.

It is not possible to process the sum signal simply by taking thederivative and by detecting the instants at which the value of thisderivative passes through 0. In practice, a system of this nature wouldgive the real extreme values on the sum channel only if this channelwere not subject to noise and such a system would be the source ofsignificant number of errors in the case of a channel on which noise ispresent, which is always the situation in practice.

An example of this sum signal, subject to noise as mentioned above, isrepresented in FIG. 7, this signal varying between two minima, S min(t1) and S min (t9), corresponding to the instants t1 and t9. Betweenthese minima, there is real maximum S max (t5) at the instant t5twofalse maxima at the instants t3 and t8 and two false minima, at theinstants t4 and t7.

In order to process a signal of this nature according to the inventionan arrangement as represented in FIG. 6 is used, which figure shows indetail the circuit 301, 303, 304, 305 and 401 previously described. Thisembodiment is described in the course of the analysis of its mode ofoperation in the presence of the signal represented in FIG. 7.

It is assumed that the minimum corresponding to the instant t1 has beenproperly detected and that the system is about to enter a phase duringwhich it seeks the maximum S max (t5).

the transition from the phase during which the minimum is being sought,with validation of the said minimum at the instant t1, takes place, asjustified later in this description, at the instant t2, which followst1, since an extreme value cannot be detected before it has been passed,so that the observed signal has therefore undergone a certain amount ofchange subsequent to this extreme value. The switches are then in thestate marked on Figure.

In the circuit 301 the signal S is applied to the input of a firstcomparator 701, of a second comparator 702 and of a double memory 703.

The first comparator 701 enables changes in the sign of the gradient ofthe signal on the sum channel to be detected. It incorporates asubtracter 708 which receives the signal S at its positive input and atits negative input via an switch i₈ the contents of a first memory 704.This memory also receives the signal S via a switch i₁ and a delaydevice 706, which applies a delay τ equal to the value of the samplinginterval necessary for the calculation. This memory 704 is reset to zeroat time t2 by a signal RAZ1 and its contents are then continuouslyupdated by the signal S which is delayed by the time τ.

If the gradient happens to be positive, the output from the subtracter708 is positive and this state is detected by a positive-signal detector709, which is connected to the subtracter 708 via an switch i₅. Thisdetector 709 then supplies a logic-state "1" on the output line 1 of thecircuit 301.

The comparator 701 also incorporates a negative-level detector 710,which is connected to the subtracter 708 by the switch i₅ when thelatter has tipped and which therefore provides a logic-state "0" on theoutput line 2 of the circuit 301 during the process of searching for amaximum, during which process it is not connected to 708.

The second comparator 702 enables the maximum detected by the comparator701 to be validated when S decreases following such a maximum. In orderto do this, it compares the signal S with the contents of the firstmemory 704, which have been weighted by a coefficient X1. Thiscoefficient is less than 1 and varies for example between 0.7 and 1,which permits validation of the detected maximum only if the signal Shas decreased, relative to this maximum, by a sufficient margin. Thesignal from the first memory 704, available at the output of theinverter i₈, is applied to a multiplier 711 which receives, in addition,the value X1 via an switch i₇. The signal S is received at the positiveinput of a subtracter 712 and the output signal from the multiplier 711is received at its negative input. The output from the subtracter 712 isapplied via an switch i₆ to a negative-signal detector 713 whichprovides, in the case where this output is negative, a logic-state "1"on the output line 3 of the circuit 301.

A positive-signal detector 714 connected to the other output of theswitch i₆ provides, when it detects a positive signal, a logic-state "1"on the output line 4 of the circuit 301 and a logic-state "0" when it isnot connected. It enables the comparator 702 to validate the minimumwhich has been detected by the comparator 701.

The control circuit 303 incorporates two inverting amplifiers 715, whoseinputs are respectively connected to the output lines 1 and 2 of thecircuit 301. The output line 3 of the circuit 301 is connected to one ofthe inputs of an AND-gate 717 and the output line 4 is connected to oneof the inputs of an AND-gate 719. The output of the inverting amplifier715 is connected on the one hand to the other input of the gate 717 andon the other hand to one of the inputs of an switch i₉. The output ofthe inverting amplifier 716 is connected on the one hand to the otherinput of the gate 719 and on the other hand to the other circuit of theswitch i₉. The outputs of the gates 719 and 717 are respectivelyconnected to the two inputs of a first OR gate 720. The output of theswitch i₉ is connected to one of the inputs of a second OR gate 718. Theoutput of the first OR gate 720 is connected to the other input of thesecond OR-gate 718 and to the control circuit of the switch i₉. Theoutput of the second OR-gate 718 corresponds to the output line 5 of thecircuit 303 and the output of the first OR gate 720 corresponds to theoutput line 6 of this circuit.

Furthermore, the double memory 703 comprises a second memory 705 whichreceives the signal S via a switch i₃ and via a delay device 707identical to the device 706. The switch i₃ is complementary to theswitch i₁ : It is open when the switch i₁ is closed and vice versa. Theoutput from this memory is applied to the other input of the inverteri₈. The outputs from the memories 704 and 705 are likewise applied toswitches i₁₈ and i₁₉, the output lines from these switches respectivelydelivering the signals S max and S min.

The circuit 401 incorporates two channels, which respectively comprise amemory 721, 722, which receives the signal θ_(b) via respectively adelay device 723, 724 identical to the device 706 and via a switch i₂,i₄, the two switches i₂, i₄ being complementary. These memories 721, 722deliver respectively the signals θ_(b)(S max) and θ_(b)(S min) via aswitch i₂₀, i₂₁.

The output line 1 of the circuit 301 triggers the switches i₁ and i₂ andthe output line 2 triggers the switches i₃ and i₄.

The output line 6 of the circuit 303 triggers the switch i₅, i₆, i₇ andi₈ and the switches i₁₈, i₁₉, i₂₀ and i₂₁.

The integrating circuit 304 incorporates two double accumulators 725 and726.

the two inputs of the accumulator 725 are respectively supplied with theoutput signal of two adders, 727 and 728. One of the inputs of the adder727 receives the signal ε_(q) via a switch i₁₀. One of the inputs of theadder 728 receives a logic "1" via a switch i₁₁.

The signal ε_(q) is also applied via a switch i₁₂ to one of the inputsof the accumulator 726. The other input of this accumulator 726 receivesthe logic "1" via a switch i₁₃. The outputs from the accumulator 726 arerespectively applied to the other input of the adders 727 and 728, via adelay device 729, 730, which is identical to the device 706, and via aswitch i₁₄, i₁₅.

The outputs from the accumulator 725 are applied to a computer 734, viaa switch i₁₆ and i₁₇ respectively. This computer provides, at twooutputs, the signals |ε_(q) | and ΔT respectively.

The output line 5 of the circuit 303 controls the switches i₁₂ and i₁₃directly, the switches i₁₀ and i₁₁ via an inverting amplifier 732 andthe switches i₁₄ and i₁₅ via an inverting amplifier 733, i₁₂ and i₁₃thus being open while i₁₀, i₁₁, i₁₄ and i₁₅ are closed and vice versa.

The output line 6 of the circuit 303 directly controls the switches i₁₆and i₁₇.

The sequence of actions performed by the system will now be described,starting from the instant t₂, at which the minimum S min (t₁) has beenvalidated.

At this instant, the memory 704 has been reset to zero by the signalRAZ1, obtained, for example by derivation from the signal on the outputline 4 validating the minimum at t₁. At the same instant too, thecomparator 701 provides a logic "1" on the output line 1 and a logic "0on the output line 2. This logic "1" in particular closes the switchesi₁ and i₂, which permits the contents of the memories 704 and 721 to becontinuously updated by the signals S and θ_(b) respectively.

In the same way the comparator 702 provides a logic "0" on the outputlines 3 and 4.

The "0" state on the output line 2 keeps the switches i₃ and i₄ open,which permits the values S min (t₁) and θ_(b) (S min) to be retained inthe memories 705 and 722 respectively, this information beingrespectively the value of the last minimum assumed by S at t₁ and thecorresponding value for the measured position of the target.

According to the logic states which thus exist at this moment at theinputs of the circuit 303, the output lines 5 and 6 of this circuit arein the "0" state, which fact accounts for the position of the variousswitches, starting from this instant t₂ (in reality t₂ +τ, to allow forthe sampling of the calculation).

During a first period, which runs from (t₂ +τ) to t₃, the signal S isincreasing and the contents of the memory 704 are therefore always lowerthan S. The comparators 701 and 702 thus maintain the logic levels whichare previously defined on the output lines 1 to 4 and under theseconditions the switches of the arrangement remain in their previousstates.

The contents on the memories 704 and 721 are therefore continuouslyupdated, while the contents of the memories 705 and 722 remain constantand equal to the values obtained for the minimum at t₁.

The switches i₁₀, i₁₁, i₁₄ and i₁₅ are closed by the logic "0" on theoutput line 5 of the circuit 303, inverted by the inverting amplifiers732 and 733.

The accumulators 725 and 726 have been reset to zero by the signal RAZ3and RAZ4 respectively. As a result, the adders 727 and 728 deliver tothe accumulator 725 only the signal |ε_(q) | and a logic "1" since theyreceive on their other input the contents of the accumulator 726, whichare nil.

This accumulator 725 thus accumulates the successive values of |ε_(q) |and a sequence of logic "1"s, which serve as clock-timing marks. On itstwo outputs it therefore provides the signals: ##EQU15##

In a second period between t₃ and t₄ the signal S decreases, from avalue S max It₃) to a value S min (t₄), which corresponds to a falseextreme value caused by noise. Therefore this value is not to bevalidated.

Under these conditions the comparator 701 detects the decreasing in thesignal S and the output line 1 changes to the logic state "0". Thischange brings about the opening of the switches i₁, i₂ and the blockingof the contents of the memories 704, 721 at the values corresponding tothe time t₃. the fall in the signal on the output line 1 enables asignal RAZ4 to be obtained, for example by differentiation, forresetting the accumulator 726 to zero.

This value of S, which remains constant, is utilised in the comparator702, for being compared with the decreasing value of S. But taking thecoefficient X₁ into account, this comparator 702 does not validate thedecreasing in S and the output line 3 remains in the "0" state. As aresult the output line 6 of the control circuit 303 remains in the "0"state but the output line 5 changes to the state "1", which brings aboutthe closing of the switches i₁₂ and i₁₃ and the opening of the switchesi₁₀, i₁₁, i₁₄ and i₁₅.

The contents of the accumulator 725 is not updated anymore, since theswitches which supply the adders 727 and 728 are open; but in contrastthe accumulator 726 receives the signals |ε_(q) | and 1 and thendelivers a₂ and n₂, such that: ##EQU16##

In a third period between t₄ and t₅ the signal S starts to increaseagain, following the false minimum S min (t₄), up to the true maximum Smax (t₅).

The comparator 701, once again detecting that S is increasing, onceagain provides a logic "1" on the output line 1 and closes the switchesi₁ and i₂ again.

The control circuit 303 reverts to its initial state. The accumulator725 once again receives |ε_(q) | and the logic "1" and in addition, viathe adders 727 and 728, the contents of the accumulator 726, which dumpsthe signals it has received between the instants t₃ and t₄. When thisdumping operation is over, the accumulator 725 accordingly contains allthe signals subsequent to the time t₂, without interruption between thetimes t₃ and t₄.

A fourth period between t₅ and t₆ is identical to the second period. Itends at that instant t₆ when the signal S becomes less than its value att₅ multiplied by the coefficient X₁ which determines the discriminationthreshold.

At this instant the comparator 702 tips and validates the maximum whichwas determined by the comparator 701 at the instant t₅. This validationappears as a logic "1" on the output line 3 and as a logic "1" on theoutput line 6 of the circuit 303.

This logic "1" on the output line 6 triggers the tipping of theinverters i₅, i₆, i₇ and i₈, for setting the circuit 301 into aconfiguration which now permits it to detect the minimum following themaximum.

This logic "1" also triggers the temporary closing of the switches i₁₈to i₂₁, which enables the signals S max, S min, θ_(b) (S max) and θ_(b)(S min) to be obtained on the output lines from the circuits 301 and401.

Finally this logic "1" permits the closing of the switches i₁₆ and i₁₇which enable the contents of the accumulator 725 to be dumped into thecomputer 734. This computer which is for example a suitably programmedmicroprocessor Type 6800 initiates the calculations defined by theformulae: ##EQU17## these calculations starting from the values of a₁and n₁ defined over the time interval t₁ to t₅.

The result of these calculations is available on the output lines fromthe circuit 304-305, with the corresponding values of S and θ on theoutput lines from the circuits 301 and 401. This same group of signalsis supplied to the other circuits of the arrangement in order tocalculate the target parameters.

The tipping of the inverters restores at the inputs of the controlcircuit 303 the logic states which, having regard to the tipping of theinverter i₉ incorporated within this circuit, place the circuit in itsinitial state at the instant t₂ when the minima corresponding to theinstant t₁ has been validated; that is to say the state in which a logic"0" is present on the output lines 5 and 6. However, this tipping issufficiently slow to enable the accumulator 725 to dump into thecomputer 734 and to permit the calculations to be performed inside thelatter, as well as to take account of the signals on the output lines ofthe circuits 301 and 401.

Under these conditions the output line 6 opens the switches i₁₆ or i₂₁again, which operation stops the transmission of the signalsrepresenting the parameters which were determined from the maxima. Thefall in this signal is also used to obtain, for example bydifferentiation, the signal RAZ3 for resetting the accumulator 725 tozero.

The fall in the signal on the output line 5 opens the switches i₁₂ andi₁₃ again, and closes the switches i₁₀, i₁₁, i₁₄ and i₁₅ again. As aresult, the accumulator 725, which has just been reset to zero, receivesthe contents of the accumulator 726, corresponding to the changes in Sbetween the instants t₅ and t₆, and starts once again to receive fromthis instant t₆ the signals |ε_(q) | and logic "1". Its contents willtherefore be complete from the maximum to the next minimum. This provesin particular that the contents of this assumulator at the instant t₂certainly included the signals corresponding to the interval between theinstant t₁ and t₂ since the phenomena had been identical at the time ofthe confirmation of the minimum at t₁, which was effected at the instantt₂.

The arrangement is therefore in the state for detecting the next minimumat t₉ by monitoring the difference between the instantaneous signal Sand this same signal delayed now contained in the memory 705, which issupplied via the switch i₃ now closed, whereas the memory 704 contains Smax (t₅), since the switch i₁ is then open. For this purpose, thecomparator 701 uses the negative-signal detector 710.

The false minimum at the instant t₇ is eliminated by the comparator 702,which uses the positive-signal detector 713. In order to accomplishthis, as the values of S are changing conversely it is necessary, inorder to eliminate the false minimum at t₇, to use a threshold X₂ whichon this occasion is greater than 1 and which in practice has a valuebetween 1 and 1.5.

During the following phases the system therefore functions in the sameway up to the instant t₉ at which it returns to the starting phasecorresponding to the instant t₁.

Compared to the known antiglint device, which yields only onemeasurement of the position of the center of mass of the target, theinvention enables an estimation of the position of the externalboundaries of the target to be obtained, whatever the composition of thetarget may be.

Thus FIG. 8 represents the results obtained for a target comprisingthree bright points, P₁, P₂ and P₃ which have a reflection coefficientrespectively equal to 1, 0.3, 0.5. These three bright points aresituated along a length of five metres, at positions which have beenmarked on the ordinate axis of the graph at the bottom of the Figure, inrelation to their center of mass placed at the origin of the axis. Aperturbing point P₄ possessing a reflection coefficient of 0.15 is alsopresent. The two graphs at the top of the Figure represent respectivelythe fluctuations on the sum channel S and on the angle-error-measurementchannel ε, as a function of time. It shows that the channels are highlyperturbed, which is normal.

An antiglint device would provide the position of the center of mass,that is to say the abscissa axis of the graph at the bottom. Thearrangement according to the invention makes it possible to obtain,starting from the measurements corresponding to the two other graphs,the estimated external boundaries, H and B, of the target, in the caseof a single plane to which our description has bee restricted. It isunderstood that the invention can also be used in a perpendicular plane,which permits the boundaries of the entire target to be defined inspace. As can be appreciated from the graph this estimate fluctuatesslightly about the effective position of the points P₁ and P₃. Thiseffectively shows that the arrangement permits these external boundariesto be determined in a manner which is only very weakly influenced by thebright points in the interior, irrespective of whether they are real,such as P₂, or whether they are perturbing point, such as P₄.

It is clear that the results which have been obtained in this way do notyield the whole of the information which would be useful for obtainingcomplete knowledge of the target. Depending on whether for example thistarget represents a single aircraft, a pair of aircrafts, or a completesquadron, the actions to be taken in practice would not be the same.

Nevertheless complementary information regarding the composition of thetarget is frequently available from other sources and the resultsprovided by the invention usefully supplement such information.

thus, in the case of a single aircraft, the center of mass which isindicated by the antiglint device is often extremely asymmetric withrespect to the physical center of this target. Thus, on approaching fromthe rear, the center of mass is in the region of the jet engine, whilein the case of a head-on approach, it is in the region of the cock-pit,although the aiming point, for example in the event of opening fire, isvery obviously located at the geometrical center of the aircraft.Starting from the external boundaries of the aircraft, our arrangementthus makes it possible to determine this geometrical center.

In the case where it is known that the situation involves two aircraftsflying company, it is of course of prime importance to track themseparately, which can be done by means of our invention, and not toshoot between them two.

Finally when a target has been detected which is manoeuvring close tothe ground or to the sea--which is easy to know--the reflection of thewaves from the ground or from the sea gives rise to a well-knownimage-effect which causes, in the case of an antiglint device, a pointlocated on the surface of the earth halfway between the aircraft and itsimage to be detected. In this case, our arrangement permits thedetermination of the position of the aircraft and of its image, and itis easy to discriminate between them, bearing in mind that the image isat a negative altitude.

These results could possibly have been obtained by means of a devicecapable of a high spectral resolution, such as a bank of filters, bycarrying out for example Fourier transformations. However, a device ofthis nature would be of a complexity out of all proportion to ourarrangement, and could be embodied only with difficulty. Moreover theposition of all the bright points would be obtained and it would benecessary to interpret them in accordance with criteria which would bevery tricky to implement.

What is claimed is:
 1. A method for improving the angular resolution ofa monopulse radar, in which the monopulse signals used by the radar fordetecting a target are processed in order to obtain a sum-signal (S), adirection-signal (θ_(b)) and a signal representing the quadratureangle-error measurement |ε_(q) |, comprising the following steps inorder to obtain a signal Δθ which measures the wingspan of thetarget:detecting a first and a second successive extreme values (S maxand S min) of the sum-signal (S); measuring the time interval (ΔT)between the instants when the two extreme values occur: integrating thequadrature angle-error signal |ε_(q) | over the time interval (ΔT):dividing by the time interval (ΔT) the result of this integration, inorder to obtain the mean value of the quadrature angle-error signal|ε_(q) |, namely |ε_(q) |, over the time interval (ΔT); calculating acoefficient ##EQU18## Ln denoting the Neperian logarithm; andmultiplicating the coefficient k₁ by the means value |ε_(q) | whichoperation yields the value of the wingspan Δθ of the target.
 2. A methodaccording to claim 1, wherein in order to obtain two further signals(θ_(A) and θ_(B)), which measure the respective direction of brightpoints on the exterior of the target, it further comprises the followingoperation:storing a first and a second value θ_(b)(S max) and θ_(b)(Smin) assumed by the direction signal θ_(b) at the instants when thesum-signal (S) assumes the first and second extreme values (S max and Smin) respectively; comparing the first and second values (θ_(b)(S max)and θ_(b)(S min)) of the direction signal, in order to obtain a unitaryvariable (s) which is equal to +1 if the first value of the directionsignal exceeds its second values and to -1 if the opposite occurs;dividing the lower extreme value (S min) of the sum-signal by its higherextreme value (S max) and multiplying this ratio by the unitary variable(s) and by 0.5; subtracting, from a signal having a value of 05., of theresult of the preceding multiplication, in order to obtain a secondcoefficient (k₂); multiplying the wingspan (Δθ) of the target by thesecond coefficient (k₂); adding the first value of the direction-signal,which corresponds to the maximum value of the sum-signal, to the result(k₂ ·Δθ) of the preceding multiplication, the result of the additionbeing the first further signal (θ_(A)); and subtracting from the firstsignal (θ_(A)) the value (Δθ) of the wingspan of the target, the resultof the subtraction being the second further signal (θ_(B)).
 3. A methodaccording to claim 1, wherein in order to further obtain aquality-coefficient (Q) in respect of the measurements which have beenperformed, it further comprises the following operations:dividing thefirst extreme value of the sum signal by its second extreme value;multiplying by the first extreme value of the sum signal the result ofthe preceding division, which operation yields the quality coefficient(Q).
 4. A method according to claim 3, wherein in order to obtain anadaptively-filtered estimate of the measurements which have beenperformed it further comprises the following operations:adding to thequality coefficient Q, a feedback signal, in order to obtain a signalQ_(r) ; delaying this signal Q_(r) by a value equal to the time interval(ΔT); multiplying the delayed signal by a coefficient (C) which iscomprised between 0 and 1, which operation yields the feedback signal;dividing the quality coefficient Q by the signal Q_(r), in order toobtain a third coefficient (k₃); and, on the measuring signal which isto be filtered:subtracting, from the measuring signal, an estimated,delayed measuring signal; multiplying the result of this subtraction, bythe third coefficient (k₃); adding, to the result of the precedingmultiplication the estimated, delayed measuring signal, which operationyields the estimated measuring signal; delaying this estimated measuringsignal, by a time equal to the time interval (ΔT), which operationyields the estimated, delayed measuring signal.
 5. An arrangement forimproving the angular resolution of a monopulse radar receiver whichfrom the signals reflected by a target supplies a sum signal (S), asignal (θ_(b)) representing the direction of the target relatively to afixed reference axis (OX) and a signal |ε_(q) | representing thequadrature angle-error measurement relatively to the antenna axis, saidarrangement comprising a device (201) which delivers a signal (Δθ)representing the wingspan of the detected target and which is composedof:means (301) for detecting and supplying two successive extremevalues, a higher value (S max) and a lower value (S min) of the sumsignal (S) with which it is fed; means (302) for calculating acoefficient ##EQU19## from the two successive extreme values of the sumsignal supplied by the detecting means, Ln denoting the function"Neperian Logarithm"; control means (303) for generating first andsecond control signals which synchronize the detecting means (301) and ameans (304) for integrating the quadrature angle-error signal (|ε_(q) |)over a time interval (ΔT) between the instants when the higher and thelower extreme value of the sum signal respectively occur, whichintegrating means (304) also supplying a signal representing the timeinterval (ΔT); a second means (305) for calculating the mean value|ε_(q) | of the quadrature angle-error signal in the time interval (ΔT);and a third means (306) for calculating the product (Δθ) of the meanvalue |ε_(q) | of the quadrature angle-error signal and of thecoefficient (k₁) from the first calculating means (302).
 6. Anarrangement according to claim 5, wherein for measuring the direction oftwo bright points (A, B) of the target with respect to the fixedreference axis (OX), it further comprises a second device (202) which iscomposed of:first means (401) for storing the values of the direction(θ_(b)) of the detected target and, when controlled by the first signalsupplied by the control means (303) of the first device (201) , fordelivering first and second values of said direction (θ_(b))corresponding respectively to the higher and lower extreme values of thesum signal (S) detected in the first device; second means (402) forcomparing the first and second values of the direction (θ_(b)) which aresupplied by the storing means (401) and for delivering a signal (s)which is equal to: +1. if the first value is higher than the secondvalue-1, if the first value is lower than the second value a third means(403) for calculating, from the output signal (s) of the comparing means(402) and from the higher and lower extreme values of the sum signal (S)supplied by the detecting means (301) of the first device (201), asecond coefficient: ##EQU20## and for calculating a quality coefficient(Q) which qualifies the measurement of the wingspan (Δθ) of the targetcarried out by the first device (201), such that Q=S max, where S max isthe higher extreme value and S min is the lower extreme value of the sumsignal; fourth means (404) for calculating and delivering the respectivedirection (θ_(A), θ_(B)) of the two bright points (A, B) at therespective extreme limits of the target, which means being supplied withthe second coefficient (k₂) from the third calculating means (403), withthe value of the direction (θ_(b)) of the target, which corresponds tothe higher extreme value of the sum signal (S) and which is delivered bythe storing means (401), and with the wingspan (Δθ) of the target whichis delivered by the first device (201).
 7. An arrangement according toclaim 6, wherein it further comprises a third device (203) foradaptively filtering the measurements carried out by the first andeventually second device, said third device comprising:means (413, 453,463) for calculating a quality coefficient (Q) which qualifies themeasurement of the wingspan (Δθ) of the target carried out by the firstdevice (201) and eventually the measurement of the direction (θ_(A)θ_(B)) of the two extremes bright points (A, B) of the target carriedout by the second device (202), which means (413, 453, 463) beingsupplied with the higher (S max) and lower (S min) extreme values of thesum signal and delivering the quality coefficient ##EQU21## means (501)for calculating a third coefficient (k₃) which is comprised between 0and 1, which means (501) being supplied with the quality coefficient (Q)from the means (413, 453, 463) and with the time interval (ΔT) from theintegrating means (304) of the first device (201); and adaptivefiltering means (512, 522, 532) supplied with the time interval (ΔT)from the integrating means (304), with the third coefficient (k₃) andrespectively with the output signal (Δθ and θ_(a), θ_(B)) from the firstdevice (201) and eventually from the second device (202), whichfiltering means (512, 522, 532) delivering an estimated value (Δθ; andθ_(A), θ_(B)) of the measurement to be filtered.
 8. An arrangementaccording to claim 5, wherein the detecting means (301) comprises:afirst memory (704), for receiving the sum signal (S) via a first switch(i₁) and a first delay device (706); a second memory (705) for receivingthe sum signal (S) via a second switch (I₃) and a second delay device(707); a first comparator (701), comprising a subtracter (708) whichreceives at its positive input the sum signal (S) and at its negativeinput, via a first inverter (i₈), the contents of the first memory (704)or of the second memory (705); a positive-signal detector (709) which isconnected, via a second inverter (i₅), to the output of the subtracter(708) and which delivers, at a first output line (1), a binary signalassuming the value "1" when a positive signal is detected andcontrolling the first switch (i₁); and a negative-signal detector (710),which is connected, by the second inverter (i₅) to the subtracter (708),and which delivers, at a second output line (2), a binary signalassuming the value "1" when a negative signal is detected andcontrolling the second switch (i₃); and a second comparator (702),comprising a subtracter (712), which receives at its positive input, thesum signal (S); a multiplier (711) which multiplies the signal deliveredby the first inverter (i₈) by a coefficient (X₁) between 0 and 1, or bya coefficient (X₂) higher than 1, these coefficients being selected bymeans of a third inverter (i₇), and which delivers the result of thismultiplication to the negative input of the subtracter (712); anegative-signal detector (713) which is connected, via a fourth inverter(i₆), to the output of the subtracter (712), and which delivers, at athird output line (3), a binary signal assuming the value "1" when anegative signal is detected; and a positive-signal detector (714), whichis connected via the inverter (i₆), to the output of the subtracter(712), and which delivers, at a fourth output line (4), a binary signalassuming the value "1" when a positive value is detected; the first,second, third and fourth inverters (i₈, i₅, i₇ , i₆) being controlled bythe first control signal from the control means (303).
 9. An arrangementaccording to claim 8, wherein the control means (303) comprises:a firstinverting amplifier (715) the input of which is connected to the firstoutput line (1) of the detecting means (301); a second invertingamplifier (716), the input of which is connected to the second outputline (2) of the detecting means (301); a first AND gate (717), the firstand second inputs of which are respectively connected to the output ofthe first inverting amplifier (715) and to the third output line (3) ofthe detecting means (301); a second AND gate (719), the first and secondinputs of which are respectively connected to the output of the secondinverting amplifier (716) and to the output line (4) of the detectingmeans (301); a first OR gate (718), a first input of which is connected,via a fifth inverter (i₉) to the output of the first or of the secondinverting amplifier (715 or 716) and the output (5) of which delivers abinary signal as the second control signal; and a second OR gate (720),a first input of which is connected to the output of the first AND gate(717), a second input of which is connected to the output of the secondAND (719) and the output line (6) of which is connected to the secondinput of the first OR gate (718) and to the control-input of theinverter (i₈), and delivers a binary control signal as the first controlsignal for controlling the first, second, third and fourth inverters(i₈, i₅, i₇, i₆) of the detecting means (301).
 10. An arrangementaccording to claim 5, wherein the integrating means (304) comprises:afirst double accumulator (725), for receiving the signal |ε_(q) | via afirst adder (727) and a first switch i₁₀) and for receiving a logic "1",via a second adder (728) and a second switch (₁₁); a third switch and anfourth switch i₁₂, i₁₃) which are controlled by the second controlsignal from the control means (303) and deliver respectively the signal|ε_(q) | and the logic "1" to a second double accumulator (726); a fifthswitch and a sixth switch (i₁₄, i₁₅) for receiving the contents of thesecond accumulator (726) via respectively a third delay device and afourth delay device (729, 730) and for delivering these contents to thefirst and second adders (727, 728) respectively; a first invertingamplifier (732), the input of which receives the second control signalfrom the control means (303) and the output of which controls the firstand second switches; a second inverting amplifier (733) the input ofwhich receives the second control signal from the control means (303)and the output of which controls the fifth and sixth switches; acomputer (734) for receiving the contents of the first doubleaccumulator via respectively a seventh switch and an eight switch (i₁₆,i₁₇), which are controlled by the first control signal, and forcalculating and delivering time interval signal (ΔT) starting from thescore of logic "1"s contained in the first accumulator, and the signal|ε_(q) | by summing the signals |ε_(q) | over the time interval (ΔT).11. An arrangement according to claim 6, wherein the storing means (401)comprises:a first memory (721) for receiving the direction signal(θ_(b)) via a first switch (i₂) and a first delay circuit (723); and asecond memory (722) for receiving the direction signal (θ_(b)) via asecond switch (i₄) and a second delay circuit (724); the first andsecond switches (i₂, i₄) being so controlled that the first and secondmemories (721, 722) deliver the values of the direction signal Q_(b)which correspond respectively to the higher and lower extreme values ofthe sum signal (S).
 12. An arrangement according to claim 6, wherein thethird calculating means (403) comprises:a divider (413) for deliveringthe ratio of the lower extreme value to the higher extreme value of thesum signal (S) which have been applied to its two inputs respectively; afirst multiplier (423) which receives at a first input an externalsignal equal to 0.5 and at a second input the output signal (s) of thecomparing means (402); a second multiplier (433) which receives at afirst input the output signal of the first multiplier (423) and at asecond input the output signal of the divider (413) and which suppliesthe negative input of; an adder (443) to the positive input of which anexternal signal equal to 0.5 is applied and the output of which suppliesthe second coefficient (k₂).
 13. An arrangement according to claim 6,wherein the fourth calculating means (404) comprises:a multiplier (414)which receives on a first input the second coefficient supplied by thethird calculating means (403) and on a second input the signal (Δθ)representing the wingspan of the target and delivered by the firstdevice (201); a first adder (424) receiving on a first input the outputsignal of the multiplier (414) and on a second input from the storingmeans (401) the value of the direction signal (θ_(b)), which correspondsto the higher extreme value of the sum signal (S), and delivering asignal (θ_(A)) which represents the direction of the first extremebright point (A) of the target; and a second adder (434) receiving on apositive input the output signal of the first adder (424) and on anegative input the signal (Δθ) which represents the wingspan of thetarget and which is supplied by the first device (201) and delivering asignal (θ_(B)) which represents the direction of the second extremebright point (B) of the target.
 14. An arrangement according to claim 7,wherein the third coefficient calculating means (501) comprises:adivider (506) which receives on a first input the quality coefficient(Q) supplied by the quality sixth coefficient calculating means (413,453, 463) and on a second input the output signal (Q_(r)) or an adder(503) which is supplied on a first input with the quality coefficient(Q) from the sixth calculating means (463) and, via a delay circuit(504) and an amplifier (505) with its own output signal (Q_(r)), thedelay applied by the delay circuit (504) being equal to the timeinterval (ΔT) supplied by the integrating means (304) of the firstdevice and the divider (506) delivering a signal which is equal to theratio of the quality coefficient (Q) to the output signal (Q_(r)) of theadder (503) and which represents the third coefficient (k₃).
 15. Anarrangement according to claim 7, wherein the adaptive filtering means(512, 522, 532) relative to each measurement to be filtered comprises inseries:a first adder (514) which receives on a negative input themeasurement to be filtered (Δθ, θ_(A), θ_(B)) and on a positive inputvia a delay circuit (513), the filtered measurement (Δθ, θ_(A) θ_(B))delivered by the filtering means; a multiplier (515) supplied with thethird coefficient (k₃) from the seventh third coefficient calculatingmeans (501) and with the output signal of the first adder (514); and asecond adder (516) which receives on a first input the output signal ofthe multiplier (515) and on a second input the delayed filteredmeasurement from the output of the delay circuit (513); the delaycircuit (513) applying a delay equal to the time interval (ΔT).